How to Calculate Goods and Services Tax on Prepayments – Business Central | Microsoft Docs

Describes how to calculate goods and services tax (GST) for partial payments or prepayments based on the total invoice amount, instead of on a partial amount.
— Read on docs.microsoft.com/en-us/dynamics365/business-central/localfunctionality/australia/how-to-calculate-goods-and-services-tax-on-prepayments